The present invention pertains generally to systems for processing emulsion coolant and more particularly to systems for processing a predominantly aqueous phase solution separated from an emulsion coolant recovered from can bodies in a can manufacturing process to recover reclaimable oil.
In the can manufacturing industry, and particularly in the aluminum beverage can manufacturing industry, cans are commonly manufactured in high speed production lines involving the steps of cupping, body making, trimming, washing, printing, internal coating and necking and flanging. In the cupping step, sheet materials, such as sheet aluminum, are lubricated with an oil and water emulsion coolant and then stamped into relatively short height and relatively large diameter cups. In the body making step, the cup is forced by a moving ram through a series of concentric ironing dies that stretch the cup to form a relatively taller height and relatively smaller diameter can body. In both the cupping and body making steps, the sheet material is covered with the coolant to lubricate the sheet material and dissipate heat generated by the process of stretching and forming the sheet material. After the can bodies have been trimmed, they are carried through a multiple stage can body washer which removes the used coolant and metal fines from the can bodies.
The used oil and water emulsion coolant recovered from the can bodies is processed for re-use to form reconstituted emulsion coolant by washing the coolant adhering to can bodies with an aqueous solution having a pH of about 2.0, as described in U.S. Pat. No. 4,027,685, issued June 7, 1977 to Heard et al., which is specifically incorporated herein by reference and forms a part of this disclosure for all that it discloses. The result is a mixture of emulsion coolant and aqueous solution which can be separated in one or more stages by heating the mixture to elevated temperatures sufficient to break a substantial portion of the emulsion into a predominantly hydrocarbon phase and a predominantly aqueous phase. The predominantly hydrocarbon phase can then be reconstituted to form an emulsifiable oil. The separated predominantly aqueous phase can be heated in subsequent stages to even higher temperatures to further separate an additional predominantly hydrocarbon phase from an additional predominantly aqueous phase or simply allowed to stand in a retention tank to allow further separation of the predominantly hydrocarbon and aqueous phases. The remaining additional predominantly aqueous phase is then normally subjected to a polymer treatment process, such as a dissolved air flotation process, in which anionic and cationic polymers attach to oil, grease, metals, suspended solids, and other waste materials, to form a sludge for solid waste disposal.
The disadvantage of such a treatment process is that a large amount of reclaimable oil is processed into sludge which produces a large volume of material for solid waste disposal. Additionally, polymer treatment costs are substantial because of the amount of oil which must be removed from the additional predominantly aqueous phase solution. Also, oil removed from the additional predominantly aqueous phase solution by the polymer treatment process essentially cannot be reclaimed from the sludge because of the manner in which the polymers are attached to the oils. Consequently, conventional processes of removing oil from predominantly aqueous phase solutions, even after several acid cracking steps, results in an expensive polymer treatment process which produces a large volume of sludge for solid waste disposal. Moreover, the sludge produced cannot be reclaimed in a manner to offset costs of the treatment process.
These problems have been overcome by the use of ultra-filtration and reverse osmosis processes wherein oily waste waters produced in various industries are accumulated in a process tank and circulated between a filtration processing system and a process tank to significantly reduce the volume of waste liquid by removing a filtered effluent (permeate) which is suitable for discharge. The concentrate (retente) from the ultra-filtration process is circulated back into the process tank to increase the waste concentration level. When the volume of waste fluid is decreased significantly, it is removed and sold to local scrap reclaimers.
This system has the advantage of eliminating treatment costs associated with polymer treatment processes and producing a permeate effluent which is suitable for disposal. The filtration process provides a consistent oil waste concentration level in the permeat effluent which does not vary with the concentration of the effluent being filtered. However, the process utilized does not allow for direct oil recovery from the concentrated waste fluid. Additionally, since batch processing is used in conventional filtration processes as described above, waste concentration levels progressively increase during the process. This causes the frequency of the filter cleaning cycle to be significantly increased.